To reproduce: Start editing an article, edit the same article in a second tab, submit the changes in the second tab, then submit the changes in the first tab.
Actual result: The resulting message says "Someone else has changed this page since you started editing it, resulting in an edit conflict."
Expected result: It should say "You have changed this page ..." (Also, perhaps the text below that should be different, since it's more likely that you intend to overwrite your own changes than someone else's that you probably weren't aware of.)